49ers Michael Crabtree makes a one handed catch from Quarterback Alex Smith. Afetr review it was later called incomplete San Francisco 49ers lead the Chicago Bears at the half 7-3 at Candlestick Park Thursday November 12, 2009.

Photo: Lance Iversen, The Chronicle

49ers Michael Crabtree makes a one handed catch from Quarterback...

Image 2 of 19

49ers head coach Mike Singletary yells directions in the final seconds of game as the San Francisco 49ers went on to beat the Chicago Bears 10-6 on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Michael Macor, The Chronicle

49ers head coach Mike Singletary yells directions in the final...

Image 3 of 19

San Francisco 49er Michael Lewis celebrates his game winning interception in the final seconds of their game with the Chicago Bears at Candlestick Park Thursday November 12, 2009 10-6

Photo: Lance Iversen, The Chronicle

San Francisco 49er Michael Lewis celebrates his game winning...

Image 4 of 19

49ers Frank Gore breaks through the line of scimage in first quarter action. The San Francisco 49ers lead the Chicago Bears 7-3 at the half Thursday November 12, 2009.

Photo: Lance Iversen, The Chronicle

49ers Frank Gore breaks through the line of scimage in first...

Image 5 of 19

San Francisco 49ers Quarterback Alex Smith is sacked in the 2nd quarter by Chicago Bears Marcus Harrison 94 and Anthony Adams 95 at Candlestick Park Thursday November 12, 2009. San Francisco 49ers lead the Chicago Bears 7-3 at the half.

Photo: Lance Iversen, The Chronicle

San Francisco 49ers Quarterback Alex Smith is sacked in the 2nd...

Image 6 of 19

49ers Frank Gore hauls in a Alex Smith pass for a first down in 2nd quarter action at Candlestick Park Thursday November 12, 2009. San Francisco 49ers leads the Chicago Bears 7-3 at the half.

Photo: Lance Iversen, The Chronicle

49ers Frank Gore hauls in a Alex Smith pass for a first down in 2nd...

Image 7 of 19

Chicago Bears Quarterback Jay Cutler tries to run away from 49ers Justin Smith late into the 4th quarter. San Francisco 49ers defeated the Chicago Bears at Candlestick Park Thursday November 12, 2009 10-6

Teammates swarm San Francisco 49ers safety Michael Lewis after he intercepted a pass with seconds left in the game as the San Francisco 49ers beat the Chicago Bears 10-6 on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Michael Macor, The Chronicle

Teammates swarm San Francisco 49ers safety Michael Lewis after he...

Image 11 of 19

San Francisco 49ers defensive tackle Aubrayo Franklin (92) celebrate his 2nd quarter inteception as the San Francisco 49ers take on the Chicago Bears on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Michael Macor, The Chronicle

San Francisco 49ers defensive tackle Aubrayo Franklin (92)...

Image 12 of 19

San Francisco 49ers quarterback Alex Smith (11) throws downfield in the 4th quarter as the San Francisco 49ers take on the Chicago Bears on Thursday November 12, 2009 in San Francisco, Calif.

San Francisco 49ers safety Mark Roman (26) returns an interception in the 4th quarter as the San Francisco 49ers take on the Chicago Bears on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Lance Iversen, The Chronicle

San Francisco 49ers safety Mark Roman (26) returns an interception...

Image 14 of 19

San Francisco 49ers running back Frank Gore (21) has the ball knocked loose by Chicago Bears cornerback Charles Tillman (33) in the 4th quarter but was recovered by San Francisco as the San Francisco 49ers take on the Chicago Bears on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Lance Iversen, The Chronicle

San Francisco 49ers running back Frank Gore (21) has the ball...

Image 15 of 19

San Francisco 49ers safety Michael Lewis (32) intercepts a pass in the end zone in the final seconds to seal the win as the San Francisco 49ers beat the Chicago Bears 10-6 on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Michael Macor, The Chronicle

San Francisco 49ers safety Michael Lewis (32) intercepts a pass in...

Image 16 of 19

San Francisco 49ers defensive end Justin Smith (94) pressures Chicago Bears quarterback Jay Cutler (6) in the 3rd quarter as the San Francisco 49ers take on the Chicago Bears on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Michael Macor, The Chronicle

San Francisco 49ers defensive end Justin Smith (94) pressures...

Image 17 of 19

San Francisco 49ers running back Frank Gore (21) scores on a 14 yard run in the 2nd quarter, chased by Chicago Bears' Danieal Manning (38) as the San Francisco 49ers take on the Chicago Bears on Thursday November 12, 2009 in San Francisco, Calif.

Photo: Michael Macor, The Chronicle

San Francisco 49ers running back Frank Gore (21) scores on a 14...

Image 18 of 19

San Francisco 49er Josh Morgan is introduced at Candlestick Park Thursday November 12, 2009 prior to their game with the Chicago Bears.

Photo: Lance Iversen, The Chronicle

San Francisco 49er Josh Morgan is introduced at Candlestick Park...

Image 19 of 19

49ers head coach Mike Singletary yells directions to his team in the final seconds of game as the San Francisco 49ers went on to beat the Chicago Bears 10-6 on Thursday November 12, 2009 in San Francisco, Calif.

In a meager offensive output for the 49ers, the low point came in the third quarter when an athletic quarterback and an offensive line averaging 320 pounds per man could not gain less than a yard.

The 49ers were at the Chicago 46-yard line, facing 4th-and-1. It was too far to attempt a field goal, and a punt at that point on the field in a home game could be seen as capitulation.

So coach Mike Singletarygave the nod to going for it. The line got no push whatsoever, and Alex Smithwas unable to find a crease to squeeze out less than a yard. The play was stuffed and the Bears took over, eventually punching across a subsequent field goal.

"I will say this: That was not a very good decision," Singletary said. "That was a bad decision on my part. Now, to answer your question, I want my offensive line to know that if we have half a yard (to go), I expect them to get it. After that play, I told them I believe in you. I don't see any reason in the world that I shouldn't expect us to make it."

Woof, woof: There was a little pregame jawing between tight end Vernon Davisand Bears defensive end Adewale Ogunleye, which is surprising because Ogunleye was the one Chicago defensive player whom Davis had something good to say about earlier in the week.

Bears center Olin Kreutzpulled Ogunleye away from Davis, and that was the end of it.

"Their defense was riled up because I called them out earlier in the week," Davis said. "That's what you want. You want the opposing team to come after you hard. There was some talk (on the field). I still managed to take care of my assignments."

Not active: Wide receiver Isaac Brucewas declared inactive for the game, ostensibly with an ankle injury that he either sustained in the Tennessee game or in practice Tuesday.

It's the clearest indication yet that the 49ers are moving in a younger direction with Michael Crabtree, Josh Morganand Jason Hill, players in their first, second and third years, respectively.

Crabtree had four receptions for 48 yards, Morgan three for 24 and Hill had one catch for five yards.

Bruce is in his 16th season. His contract with the 49ers expires after this season.

Additionally, right cornerback Shawntae Spencersaid he sustained a mild concussion in the game.

Briefly: Former 49ers tackle Bubba Parisserved as an honorary captain for the game. ... Thursday night's game marked the first time in more than 23 years that five different 49ers had interceptions. In a Sept. 7, 1986 game at Tampa Bay, the 49ers recorded seven interceptions against the Bucs and Steve DeBerg. ... Safety Roman's interception in the fourth quarter was his first since Dec. 14, 2006. ... Frank Gore notched his 17th 100-yard rushing game with 104 yards. Joe Perryhas the franchise record for 100-yard games with 20.